Material application systems are used to apply one or more materials in one or more layers to an object. General examples are powder coating systems, other particulate material application systems such as may be used in the food processing and chemical industries. These are but a few examples of a wide and numerous variety of systems used to apply particulate materials to an object.
The application of dry particulate material is especially challenging on a number of different levels. An example, but by no means a limitation on the use and application of the present inventions, is the application of powder coating material to objects using a powder spray gun. Because sprayed powder tends to expand into a cloud or diffused spray pattern, known powder application systems use a spray booth for containment. Powder particles that do not adhere to the target object are generally referred to as powder overspray, and these particles tend to fall randomly within the booth and will alight on almost any exposed surface within the spray booth. Therefore, cleaning time and color change times are strongly related to the amount of surface area that is exposed to powder overspray.
There are two generally known types of dry particulate material transfer processes, referred to herein as dilute phase and dense phase. Dilute phase systems utilize a substantial quantity of air to push material through one or more hoses or other conduit from a supply to a spray applicator. A common pump design used in powder coating systems is a venturi pump which introduces a large volume of air under pressure and higher velocity into the powder flow. In order to achieve adequate powder flow rates (in pounds per minute or pounds per hour for example), the components that make up the flow path must be large enough to accommodate the flow with a high air to material ratio (in other words lean flow) otherwise significant back pressure and other deleterious effects can occur.
Dense phase systems on the other hand are characterized by a high material to air ratio (in other words a “rich” flow). A dense phase pump is described in U.S. Pat. No. 7,150,585, issued on Dec. 19, 2006, filed under Ser. No. 10/501,693 on Jul. 16, 2004 for PROCESS AND EQUIPMENT FOR THE CONVEYANCE OF POWDERED MATERIAL, the entire disclosure of which is fully incorporated herein by reference, and which is owned by the assignee of the present inventions. This pump is characterized in general by a pump chamber that is partially defined by a gas permeable member. Material, such as powder coating material as an example, is drawn into the chamber at one end by gravity and/or negative pressure and is pushed out of the chamber through an opposite end by positive air pressure. This pump design is very effective for transferring material, in part due to the novel arrangement of a gas permeable member forming part of the pump chamber.